The present invention relates to a hydraulic circuit for recovering energy, which circuit comprises at least one hydraulic motor, two main ducts for feeding fluid to or discharging fluid from said at least one motor, a low-pressure fluid source, a high-pressure accumulator forming a high-pressure fluid source, and valve means suitable for taking up an energy recovery configuration in which said valve means respectively connect the feed main duct to the low-pressure fluid source and connect the discharge main duct to the high-pressure accumulator, and an energy delivery configuration in which said valve means respectively connect the feed main duct to the high-pressure accumulator and connect the discharge main duct to the low-pressure fluid source.
It is known that such circuits can be fitted to vehicles for the purpose of limiting energy consumption. Such vehicles are “hybrid” vehicles, each such vehicle having a conventional propulsion engine (e.g. of the internal combustion engine type) and a circuit of the above-mentioned type in which the hydraulic motor(s) can be coupled mechanically to the propulsion device, e.g. by being coupled to the drive outlet of said device, or indeed to a wheel of the vehicle. At cruising speed, the vehicle is normally driven by its conventional propulsion engine. Energy recovery takes place during braking, during which the hydraulic motor is driven by the propulsion of the vehicle that is being braked, so that said hydraulic motor operates as a pump and feeds the high-pressure accumulator with fluid. Energy delivery takes place in particular during an acceleration phase, during which the vehicle is accelerating and during which the hydraulic motor is activated once again and is fed with high-pressure fluid coming from the accumulator, so as to deliver drive torque for assisting propulsion of the vehicle.
Such “hybrid” systems are known to be advantageous in reducing fuel consumption.
In order for the system to be genuinely effective, it is necessary for the hydraulic motor not to generate any significant resistive torque when it is deactivated, and for it to be simple and quick to put the motor into the various configurations using control means that are compact and inexpensive.
An object of the present invention is to improve the state of the art in order to achieve the above-mentioned objectives.
This object is achieved by the fact that the hydraulic motor is suitable for being declutched or for being clutched by fluid pressure, by the fact that the valve means comprise a hydraulic valve comprising firstly a valve body having a feed port connected to the feed main duct, a discharge port connected to the discharge main duct, a low-pressure link port connected to the low-pressure fluid source, a high-pressure link port connected to the high-pressure accumulator, and an auxiliary port, and secondly a slide suitable for taking up, inside the body, a neutral position in which the feed port and the discharge port communicate with each other and with the auxiliary port, an energy recovery position in which the feed port is connected to the low-pressure link port while the discharge port is connected to the high-pressure link port, and an energy delivery position in which the feed port is connected to the high-pressure link port while the discharge port is connected to the low-pressure link port, and by the fact that the hydraulic circuit further comprises control and selection means suitable for causing the slide to move from its neutral position towards its energy recovery position on receiving a first control signal, for causing the slide to move from its neutral position towards its energy delivery position on receiving a second control signal, and for causing the auxiliary port to be connected to a pressure-free enclosure or to a clutch fluid source for clutching the hydraulic motor on receiving a selection signal.
The hydraulic motor has pistons, in particular extending radially relative to the axis of rotation of its rotor, which pistons co-operate with a cam to generate the drive torque. Clutching the motor consists in placing the pistons in contact with the cam, while declutching it consists in moving them away therefrom. It can be understood that, in the declutched state, the motor does not generate any resistive torque. In the same hydraulic valve, the valve means comprise a slide that is mounted to move in the valve body between positions corresponding to the energy recovery configuration and to the energy delivery configuration, and into a neutral position in which, depending on whether the auxiliary port is connected to the pressure-free enclosure or to the clutch fluid source, the motor can be declutched or clutched. The means making it possible to obtain these various positions are thus extremely compact and can be provided at reasonable cost. It is simple to perform the control for going between the various configurations because issuing control signals makes it possible to obtain the energy recovery or the energy delivery configurations, and the selection signal makes it possible to go between the motor clutched and the motor declutched configurations.
Advantageously, the neutral position of the slide is intermediate between the energy recovery position and the energy delivery position.
This makes it possible to go very rapidly back from the neutral position to one of the energy recovery and energy delivery positions.
Advantageously, the hydraulic valve has a first control chamber suitable for being fed with fluid via a first control port so as to urge the slide to move towards its energy recovery position, and a second control chamber suitable for being fed with fluid via a second control port so as to urge the slide to move towards its energy delivery position, and the circuit further comprises solenoid valve means suitable for connecting the two control ports to a pressure-free enclosure in the absence of a control signal, for connecting the first control port to a pilot fluid source on receiving the first control signal, and for connecting the second control port to the pilot fluid source on receiving the second control signal.
These control means for controlling the hydraulic valve are simple and reliable, and are of reasonable construction cost.
Advantageously, the solenoid valve means comprise a first pilot solenoid valve suitable, in the rest position, for connecting the first control port to the pressure-free enclosure and, in the activated position, for connecting said first port to the pilot fluid source, and a second pilot solenoid valve suitable, in the rest position, for connecting the second control port to the pressure-free enclosure and, in the activated position, for connecting said second port to the pilot fluid source.
The auxiliary port is advantageously one of the control ports.
Thus, the pilot fluid also serves as clutch fluid, thereby simplifying the circuit.
It is then advantageous for the solenoid valve means to be suitable for connecting both of the control ports to the pilot fluid source on jointly receiving first and second control signals issued together.
This joint reception makes it possible to obtain the neutral position and to obtain clutching of the motor, whereas said neutral position is obtained when the motor is in the declutched state while neither of the two signals is issued.
In a variant, the circuit advantageously further comprises a declutching solenoid valve suitable for taking up a declutching position in which it connects the auxiliary port to a pressure-free enclosure and a clutching position in which it connects the auxiliary port to the clutch fluid source.
In which case, the declutching is obtained by the specific declutching solenoid valve, which is controlled independently from the feeding of the control ports of the hydraulic valve.
Advantageously, the internal space(s) of the casing(s) of the hydraulic motor(s) is/are put under pressure, e.g. by being connected to the clutch fluid source via a constriction.
This putting under pressure makes it possible to go from the motor clutched state to the motor declutched state, because the pressure inside the casing tends to push back the pistons towards the end walls of their cylinders. As is known, other systems could be used to push back the pistons, e.g. springs.
The fact that the internal space of the casing is put under pressure from the clutch fluid source but via a constriction makes it possible to be certain of obtaining a pressure inside said internal space that is lower than the pressure used for performing the clutching, because of the head loss achieved by the constriction, and without however requiring the use of another fluid source.
The circuit of the invention, equipping a vehicle having a propulsion device to which said at least one hydraulic motor is suitable for being mechanically coupled, can be controlled by a method that comprises at least the following control steps:                issuing a first control signal for performing an energy recovery phase during which said at least one hydraulic motor is clutched while the vehicle as driven by the propulsion device is decelerating;        ceasing to issue the first control signal for performing a balancing phase during which the feed and discharge main ducts communicate with each other;        issuing a second control signal for performing an energy delivery phase during which the hydraulic motor is clutched while the vehicle as driven jointly by the propulsion device and by said at least one hydraulic motor is accelerating; and        ceasing to issue the second control signal for performing a standby phase during which the feed and discharge main ducts communicate with each other, and during which said at least one hydraulic motor is declutched.        
While the vehicle is in a deceleration phase, the motor operates as a pump so that the feed main duct is at a pressure lower than the pressure at which the discharge main duct finds itself, which discharge main duct then feeds the high-pressure accumulator. Conversely, the pressure states are the reverse during an energy delivery phase, during which the feed duct is at a pressure higher than the pressure in the discharge duct. Performing a balancing phase between the energy recovery and energy delivery phases makes it possible to balance the pressures in the feed and discharge main ducts of the motor, thereby preventing the reversal of the above-mentioned pressure states from taking place too suddenly.
Advantageously, the balancing phase includes a first period during which said at least one hydraulic motor remains clutched, and, if it is established that said first period has ended, said first period is followed by a second period during which said at least one hydraulic motor is declutched, and at the end of which said at least one hydraulic motor is clutched again.
The fact that the motor remains clutched during the first period of the balancing phase makes it possible to go very rapidly to the energy delivery phase or to another energy recovery phase if necessary. Conversely, if, it is established that the first period has ended before it is necessary to go over to the energy delivery phase, declutching the hydraulic motor makes it possible to avoid unnecessarily overloading said hydraulic motor, and especially avoids generating drag torque giving rise to efficiency losses.
For example, the end of the first period is established by comparing the elapsed time of the balancing phase with a reference lapse of time, which can be a predetermined lapse of time, or else the deceleration lapse of time, or indeed a fraction thereof. It can also be established when a desired pressure for the charging of the high-pressure accumulator is reached.
Advantageously, in order to clutch said at least one hydraulic motor, the auxiliary port of the hydraulic valve is connected to the clutch fluid source, and the connection between the auxiliary port and the clutch fluid source is maintained during at least one of the energy recovery and energy delivery phases.
This makes it possible to ensure that the motor remains clutched, without requiring any particular control signal to be issued, at the end of the energy recovery and/or energy delivery phase during which the connection between the auxiliary port and the clutch fluid source has been maintained. It is thus possible, in particular, to avoid briefly going via declutching or a commencement of declutching after said phase, when the balancing phase starts.